Method and apparatus for transmitting reception confirmation response of user equipment in wireless communication system

ABSTRACT

Provided is a method for transmitting a HARQ (hybrid automatic repeat request) ACK (acknowledgment)/NACK (not-acknowledgement) response from user equipment in which two serving cells are set. The method comprises the steps of: receiving a first transport block through a first serving cell which is set in a first transmission mode, in which up to two transport blocks are supported; determining an HARQ ACK/NACK response which includes a first response to the first transport block; and transmitting the HARQ ACK/NACK response, wherein the first response is the same as a response used when two transport blocks have been received through the first serving cell.

TECHNICAL FIELD

The present invention relates to wireless communication and, moreparticularly, to a method and apparatus in which user equipment sends aHybrid Automatic Repeat Request (HARQ) acknowledgement(ACK)/not-acknowledgement (NACK) response, that is, an ACK/NACKresponse, in a wireless communication system.

BACKGROUND ART

A multi-carrier system has recently been in the spotlight. Themulti-carrier system means a system which supports a broadband bycollecting one or more Component Carriers (CCs), each having a bandwidthsmaller than the broadband, that is, a target when a wirelesscommunication system supports the broadband. That is, a plurality ofcomponent carriers can be used in a multi-carrier system. The componentcarrier is defined by a center frequency and a bandwidth.

A component carrier on which a base station sends a signal to a terminalis called a downlink component carrier, and a component carrier on whicha terminal sends a signal to a base station is called an uplinkcomponent carrier. One uplink component carrier and one downlinkcomponent carrier correspond to one cell. Accordingly, it can be saidthat a terminal supplied with service using a plurality of downlinkcomponent carriers is supplied with the service from a plurality ofserving cells.

In a multi-carrier system, the number of uplink control signalstransmitted can be increased as compared with the existing singlecarrier system. For example, in a multi-carrier system, a terminalcannot receive a plurality of Transport Blocks (TBs) through a pluralityof downlink component carriers. In this case, the number of uplinkcontrol signals can be increased as compared with a single carriersystem because the terminal must send a Hybrid Automatic Repeat Request(HARQ) acknowledgement/non-acknowledgement (ACK/NACK), that is, anACK/NACK response, to each of the transport blocks. Furthermore, in amulti-carrier system, there may be a limit that an uplink control signalhas to be transmitted through one uplink component carrier. Accordingly,there is a need for a method that is different from a method of sendingan uplink control signal in the existing single carrier system becauseincreased uplink control signals may have to be transmitted through oneuplink component carrier.

Furthermore, in a multi-carrier system, a transport block that can betransmitted through one downlink component carrier may differ accordingto a transmission mode. For example, only one transport block can betransmitted or a maximum of two transport blocks can be transmitted in aphysical downlink shared channel (PDSCH) depending on transmission modeof a downlink component carrier. Furthermore, there may be a case whereonly one transport block is transmitted through a downlink componentcarrier set in transmission mode in which a maximum of two transportblocks can be transmitted. In this case, how a terminal will send HARQACK/NACK using what method may be problematic.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusin which user equipment sends an HARQ ACK/NACK response in a wirelesscommunication system.

Technical Solution

A method in accordance with an aspect of the present invention providesa method in which user equipment in which two serving cells have beenconfigured sends an HARQ ACK/NACK response. The method includes thesteps of receiving a first transport block through a first serving cellset in a first transmission mode supporting up to two transport blocks;determining an HARQ ACK/NACK response comprising a first response to thefirst transport block; and sending the HARQ ACK/NACK response, whereinthe first response is identical with a response used when the twotransport blocks are received through the first serving cell.

The first response may be identical with a response when all the twotransport blocks have been received and successfully decoded in thefirst serving cell, if the first transport block has been successfullydecoded.

The first response may be identical with a response when all the twotransport blocks have not been successfully decoded in the first servingcell, if the first transport block has not been successfully decoded.

The method may further include the step of receiving at least one secondtransport block through a second serving cell set in a secondtransmission mode, wherein the HARQ ACK/NACK response may include afirst response to the first transport block and a second response to theat least one second transport block.

The steps of determining two uplink radio resources for the firsttransport block; determining at least one uplink radio resource for theat least one second transport block; selecting any one of the two uplinkradio resources and the at least one uplink radio resource in responseto the first response and the second response; and sending informationof 2 bits in the selected one uplink radio resource may be furtherincluded.

If the first serving cell is a primary cell, the two uplink radioresources may carry resource allocation information on the firsttransport block and the two uplink radio resources may be determinedbased on radio resources used in a Physical Downlink Control Channel(PDCCH) transmitted through the first serving cell.

If the second serving cell is a secondary cell, the at least one uplinkradio resource may be determined based on a radio resource valuedetermined by a PDCCH transmitted by the second serving cell, from amongfour radio resource values designated according to a higher layerconfiguration.

The information of 2 bits may be modulated according to QuadraturePhase-Shift Keying (QPSK) and transmitted.

If the second transmission mode is transmission mode supporting up totwo transport blocks and the one second transport block is receivedthrough the second serving cell and is successfully decoded, the secondresponse may be identical with a response when all the two transportblocks have been successfully decoded in the second serving cell.

If the second transmission mode is transmission mode supporting up totwo transport blocks and the one second transport block is receivedthrough the second serving cell and is not successfully decoded, thesecond response may be identical with a response when all the twotransport blocks have not been successfully decoded in the secondserving cell.

The first serving cell may be a primary cell through which the userequipment performs an initial connection establishment process or aconnection re-establishment process with a base station.

The two serving cells may operate in Frequency Division Duplex (FDD).

User equipment in accordance with another aspect of the presentinvention includes a Radio Frequency (RF) unit for sending or receivingradio signals and a processor connected to the RF unit, wherein theprocessor receives a first transport block through a first serving cellset in a first transmission mode supporting up to two transport blocks,determines an HARQ ACK/NACK response comprising a first response to thefirst transport block, and sends the HARQ ACK/NACK response, and thefirst response may be identical with a response used when the twotransport blocks are received through the first serving cell.

The processor may receive at least one second transport block throughthe second serving cell set in a second transmission mode, and the HARQACK/NACK response may include a first response to the first transportblock and a second response to the at least one second transport block.

Advantageous Effects

An HARQ ACK/NACK response can be transmitted without error even when thetransmission mode of a serving cell set in UE is changed. Furthermore,an HARQ ACK/NACK response can be transmitted while reducing apossibility that an error may occur by separating points on a signalconstellation to which an HARQ ACK/NACK response is mapped to a maximumextent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows the structure of a radio frame used in 3GPP LTE.

FIG. 3 shows an example of a resource grid for one downlink slot.

FIG. 4 shows the structure of a downlink subframe in 3GPP LTE.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 shows a relationship in which PUCCH formats are physically mappedto control regions.

FIG. 7 shows a PUCCH format 1b in a normal CP in 3GPP LTE.

FIG. 8 shows an example of the execution of an HARQ.

FIG. 9 shows an example of the constellation mapping of an ACK/NACKsignal in PUCCH formats 1a/1b.

FIG. 10 shows an example of a comparison between the existing singlecarrier system and a multi-carrier system.

FIG. 11 shows an example of channel selection for ACK/NACK informationof 2 bits.

FIG. 12 illustrates channel selection for ACK/NACK information of 3bits.

FIG. 13 is an example illustrating objects indicated by the respectivebits of 3-bit ACK/NACK information and channel selection for the 3-bitACK/NACK information.

FIG. 14 is another example illustrating a mapping relationship withobjects indicated by respective bits in 3-bit ACK/NACK information.

FIG. 15 illustrates channel selection for ACK/NACK information of 4bits.

FIG. 16 shows examples illustrating a mapping relationship with objectsindicated by the respective bits of 4-bit ACK/NACK information.

FIG. 17 shows mapping to radio resources and constellation points when4-bit ACK/NACK information is information, such as that shown in FIG.16.

FIG. 18 is another example illustrating a mapping relationship withobjects indicated by respective bits in 4-bit ACK/NACK information andmapping to radio resources and constellation points.

FIG. 19 is the ACK/NACK transmission method of UE in accordance with anembodiment of the present invention.

FIGS. 20 to 22 show examples in which UE uses channel selection when onetransport block is received in a serving cell which supports up to twotransport blocks.

FIG. 23 is a block diagram showing a BS and UE in which an embodiment ofthe present invention is implemented.

MODE FOR INVENTION

The following technology may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), andSingle Carrier Frequency Division Multiple Access (SC-FDMA). CDMA may beimplemented using radio technology, such as Universal Terrestrial RadioAccess (UTRA) or CDMA2000. TDMA may be implemented using radiotechnology, such as Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented using radio technology, suchas Institute of Electrical and Electronics Engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or Evolved UTRA (E-UTRA).IEEE 802.16m is the evolution of IEEE 802.16e, and it provides backwardcompatibility with systems based on IEEE 802.16e. UTRA is part of aUniversal Mobile Telecommunications System (UMTS). 3^(rd) GenerationPartnership Project (3GPP) Long Term Evolution (LTE) is part of anEvolved UMTS (E-UMTS) using Evolved-UMTS Terrestrial Radio Access(E-UTRA), and 3GPP LTE adopts OFDMA in downlink and adopts SC-FDMA inuplink. LTE-Advance (LTE-A) is the evolution of 3GPP LTE. In order toclarify a description, IEEE 802.16m is chiefly described, but thetechnical spirit of the present invention is not limited thereto.

FIG. 1 shows a wireless communication system.

The wireless communication system 10 includes one or more Base Stations(BSs) 11. The BSs 11 provide communication services to respectivegeographical areas (commonly called cells) 15 a, 15 b, and 15 c. Thecell may be divided into a plurality of regions (called sectors). UserEquipment (UE) 12 may be fixed or mobile and also be called anotherterminology, such as a Mobile Station (MS), a Mobile Terminal (MT), aUser Terminal (UT), a Subscriber Station (SS), a wireless device, aPersonal Digital Assistant (PDA), a wireless modem, or a handhelddevice. The BS 11 commonly refers to a fixed station communicating withthe MSs 12, and the BS may also be called another terminology, such asan evolved NodeB (eNB), a Base Transceiver System (BTS), or an accesspoint.

This technology can be used in downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS11.

The wireless communication system may be any one of a Multiple-InputMultiple-Output (MIMO) system, a Multiple-Input Single-Output (MISO)system, a Single-Input Single-Output (SISO) system, and a Single-InputMultiple-Output (SIMO) system. An MIMO system uses a plurality oftransmit antennas and a plurality of receive antennas. An MISO systemuses a plurality of transmit antennas and one receive antenna. An SISOsystem uses one transmit antenna and one receive antenna. An SIMO systemuses one transmit antenna and a plurality of receive antennas.Hereinafter, a transmit antenna means a physical or logical antenna usedto send one signal or stream, and a receive antenna means a physical orlogical antenna used to receive one signal or stream.

FIG. 2 shows the structure of a radio frame used in 3GPP LTE.

Referring to FIG. 2, the radio frame includes 10 subframes, and onesubframe includes two slots. The slots within the radio frame areassigned slot numbers from #0 to #19. The time taken for one subframe tobe transmitted is called a Transmission Time Interval (TTI). The TTI maybe a scheduling unit for data transmission. For example, the length ofone radio frame may be 10 ms, the length of one subframe may be 1 ms,and the length of one slot may be 0.5 MS.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing. (OFDM) symbols in the time domain and includes a pluralityof subcarriers in the frequency domain. The OFDM symbol is forrepresenting one symbol period because 3GPP LTE uses OFDMA in downlinkand may be called another terminology depending on a multi-accessmethod. For example, if SC-FDMA is used as an uplink multi-accessmethod, the OFDM symbol may be called an SC-FDMA symbol. The structureof the radio frame is only an example. Accordingly, the number ofsubframes included in a radio frame, the number of slots included in asubframe, or the number of OFDM symbols included in a slot may bechanged in various manners.

In 3GPP LTE, one slot is defined to include 7 OFDM symbols in a normalCyclic Prefix (CP), and one slot is defined to include 6 OFDM symbols inan extended CP.

A wireless communication system can be basically divided into aFrequency Division Duplex (TDD) method and a Time Division Duplex (TDD)method. In accordance with the FDD method, uplink transmission anddownlink transmission are performed while occupying different frequencybands. In accordance with the TDD method, uplink transmission anddownlink transmission are performed at different points of time whileoccupying the same frequency band.

FIG. 3 shows an example of a resource grid for one downlink slot.

The downlink slot includes a plurality of OFDM symbols in the timedomain and includes an N_(RB) number of Resource Blocks (RBs) in thefrequency domain. The resource block is a resource allocation unit, andthe RB includes a plurality of contiguous subcarriers in one slot. Thenumber of resource blocks N_(RB) included in a downlink slot depends ona downlink transmission bandwidth configured in a cell. For example, inan LTE system, the number of resource blocks N_(RB) may be any one of 60to 110.

Each of elements on a resource grid is referred to as a Resource Element(RE). The resource element on the resource grid may be identified by anindex pair (k,l) within a slot. Here, k (k=0, N_(RB)×12-1) is asubcarrier index within the frequency domain, and I (I=0, . . . , 6) isan OFDM symbol index within the time domain.

Here, one resource block is illustrated as including 7×12 resourceelements, including 7 OFDM symbols in the time domain and 12 subcarriersin the frequency domain, but the number of OFDM symbols and the numberof subcarriers within the resource block are not limited thereto. Thenumber of OFDM symbols and the number of subcarriers may be changed invarious manners depending on the length of a CP, frequency spacing, etc.For example, in the case of a normal CP, the number of OFDM symbols is7, and in the case of an extended CP, the number of OFDM symbols is 6.In one OFDM symbol, one of 128, 256, 512, 1024, 1536, and 2048 may beselected and used as the number of subcarriers. The structure of anuplink slot may be the same as that of the downlink slot.

FIG. 4 shows the structure of a downlink subframe in 3GPP LTE.

The downlink subframe includes 2 slots in the time domain, and each slotincludes 7 OFDM symbols in a normal CP. A maximum of former 3 OFDMsymbols (a maximum of 4 OFDM symbols for a 1.4 MHz bandwidth) in a firstslot within a subframe become a control region to which control channelsare allocated, and the remaining OFDM symbols become a data region towhich data channels are allocated.

The control channel includes a PDCCH (physical downlink control channel)for example. The PDCCH can carry the resource allocation and transportformat of a Downlink-Shared Channel (DL-SCH), information on theallocation of resources on an Uplink Shared Channel (UL-SCH), paginginformation, system information, and the resource allocation of a higherlayer control message, such as a random access response transmitted on aphysical downlink shared channel (PDSCH), a set of transmission powercontrol commands for individual UE within a specific UE group, and theactivation of a Voice over Internet Protocol (VoIP).

A plurality of PDCCHs can be transmitted within the control region, andan MS can monitor a plurality of PDCCHs. A PDCCH is transmitted on oneControl Channel Element (CCE) or an aggregation of some contiguous CCEs.A CCE is a logical allocation unit used to provide a PDCCH with a codingrate according to the state of a radio channel. A CCE corresponds to aplurality of Resource Element Groups (REGs). The REG can include 4 Res.The format of a PDCCH and the number of bits of a possible PDCCH aredetermined depending on a correlation between the number of CCEs and acoding rate provided by the CCEs.

A BS determines the format of a PDCCH based on Downlink ControlInformation (DCI) to be transmitted to UE and attaches a CyclicRedundancy Check (CRC) to the DCI. A unique identifier (a Radio NetworkTemporary Identifier (RNTI)) is masked to the CRC depending on the owneror use of the PDCCH. If the PDCCH is for specific UE, an identifierunique to the UE, for example, a Cell-RNTI (C-RNTI), can be masked tothe CRC. Or, if the PDCCH is for a paging message, a paging indicationidentifier, that is, a Paging-RNTI (P-RNTI), can be masked to the CRC.If the PDCCH is for a System Information Block (SIB), a systeminformation identifier, that is, a System Information-RNTI (SI-RNTI),can be masked to the CRC. A Random Access-RNTI (RA-RNTI) can be maskedto the CRC in order to indicate a random access response, that is, aresponse to the transmission of the random access preamble of UE.

The data channel includes a PDSCH. Data, system information nottransmitted through a physical broadcast channel (PBCH), a pagingmessage, etc. are transmitted in the PDSCH. The data is transmitted foreach Transport Block (TB). Each TB corresponds to a MAC layer ProtocolData Unit (PDU).

FIG. 5 shows the structure of an uplink subframe.

The uplink subframe can be divided into a control region and a dataregion in the frequency domain. A Physical Uplink Control Channel(PUCCH) on which uplink control information is transmitted is allocatedto the control region. A Physical Uplink Shared Channel (PUSCH) on whichdata and/or uplink control information are transmitted is allocated tothe data region. If this is indicated in a higher layer, UE can supportthe simultaneous transmission of a PUSCH and a PUCCH.

A PUSCH is mapped to an Uplink Shared Channel (UL-SCH), that is, atransport channel. Uplink data transmitted on the PUSCH can betransmitted for each transport block. The uplink data can be multiplexeddata. The multiplexed data can be obtained by multiplexing the transportblock for the UL-SCH and control information. The control informationmultiplexed into the data may include, for example, a Channel QualityIndicator (CQI), a Precoding Matrix Indicator (PMI), and a RandIndicator (RI). Or, the uplink data may include only controlinformation.

A PUCCH for one MS is allocated in the form of Resource Block pair (RBpair) in a subframe. Resource blocks that belong to a RB pair occupydifferent subcarriers in a first slot and a second slot. A frequencyoccupied by resource blocks that belong to a RB pair allocated to aPUCCH is changed on the basis of a slot boundary. This is said that theRB pair allocated to the PUCCH has been frequency-hopped at the slotboundary. A frequency diversity gain can be obtained when UE transmitsuplink control information through different subcarriers over time.

A PUCCH carries a variety of pieces of control information depending ona format. A PUCCH format 1 carries a Scheduling Request (SR). Here, anOn-Off Keying (OOK) method may be used. A PUCCH format 1a carriesacknowledgement/not-acknowledgement (ACK/NACK) modulated according to aBinary Phase Shift Keying (BPSK) scheme in relation to one codeword. APUCCH format 1b carries ACK/NACK modulated according to a QuadraturePhase Shift Keying (QPSK) scheme in relation to two codewords (transportblocks). A PUCCH format 2 carries a Channel Quality Indicator (CQI)modulated according to a QPSK scheme. PUCCH formats 2a and 2b carry aCQI and ACK/NACK.

Table 1 shows modulation schemes according to the PUCCH formats and thenumber of bits within a subframe.

TABLE 1 PUCCH Modulation Number of bits format scheme per subframe,M_(bit) 1 N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2bQPSK + QPSK 22

Table 2 shows the number of OFDM symbols used as a reference signal perslot in the PUCCH formats.

TABLE 2 PUCCH format Normal cyclic prefix Extended cyclic prefix 1, 1a,1b 3 2 2 2 1 2a, 2b 2 N/A

Table 3 shows the positions of OFDM symbols to which reference signalsare mapped in the PUCCH formats.

TABLE 3 set of values for ρ PUCCH format Normal cyclic prefix Extendedcyclic prefix 1, 1a, 1b 2, 3, 4 2, 3 2, 2a, 2b 1, 5 3

FIG. 6 shows a relationship in which the PUCCH formats are physicallymapped to control regions.

m is a position index that indicates the position of the logicalfrequency domain of a resource block pair allocated to a PUCCH in asubframe. The PUCCH formats 2/2a/2b are mapped to a resource block(e.g., m=0,1 in a PUCCH region) at the edge of a band and transmitted. Amixed PUCCH Resource Block (RB) may be mapped to a resource block (e.g.,m=2) that is adjacent in the direction of the center of the band in theresource block to which the PUCCH formats 2/2a/2b are allocated andtransmitted. The PUCCH formats 1/1a/1b in which an SR and ACK/NACK aretransmitted may be disposed in a resource block where m=4 or m=5. UE maybe informed of the number of resource blocks N⁽²⁾ _(RB) used in thePUCCH formats 2/2a/2b in which a CQI is transmitted through a broadcastsignal.

All the PUCCH formats use the Cyclic Shift (CS) of a sequence in eachOFDM symbol. A cyclic-shifted sequence is generated by cyclic-shifting abase sequence by a specific CS amount. The specific CS amount isindicated by a CS index.

An example in which the base sequence r_(u)(n) is defined is as follows.

r _(u)(n)=e ^(jb(n)π/4)  [Equation 1]

In Equation 1, u is a root index, n is an element index, 0≦n≦N−1, and Nis the length of the base sequence. b(n) is defined in section 5.5 of3GPP TS 36.211 V8.7.0.

The length of a sequence is equal to the number of elements included inthe sequence. u can be determined by a cell identifier (ID); a slotnumber within a radio frame, etc. When it is said that a base sequenceis mapped to one resource block in the frequency domain, the length ofthe base sequence becomes 12 because one resource block includes 12subcarriers. Another base sequence is defined depending on a differentroot index.

A cyclic-shifted sequence r(n, I_(cs)) can be generated bycyclic-shifting the base sequence r(n) as in Equation 2.

$\begin{matrix}{{{r( {n,I_{cs}} )} = {{r(n)} \cdot {\exp( \frac{{j2\pi}\; I_{cs}n}{N} )}}},\mspace{14mu} {0 \leq I_{cs} \leq {N - 1}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

In Equation 2, I_(cs) is a CS index indicating a CS amount(0≦I_(CS)≦N−1).

An available CS index of a base sequence refers to a CS index that canbe derived from the base sequence according to a CS interval. Forexample, if the length of a base sequence is 12 and a CS interval is 1,the total number of available CS indices of the base sequence is 12. Or,if the length of a base sequence is 12 and a CS interval is 2, the totalnumber of available CS indices of the base sequence is 6.

FIG. 7 shows the PUCCH format 1b in a normal CP in 3GPP LTE.

One slot includes 7 OFDM symbols, and 3 of the 7 OFDM symbols areReference Signal (RS) OFDM symbols for a reference signal, and 4 of the7

OFDM symbols are data OFDM symbols for an ACK/NACK signal.

In the PUCCH format 1b, an encoded 2-bit ACK/NACK signal is modulatedaccording to Quadrature Phase Shift Keying (QPSK), thereby generating amodulation symbol d(0).

A CS index I_(CS) may differ depending on a slot number n_(s) within aradio frame and/or a symbol index I within a slot.

In a normal CP, one slot includes four data OFDM symbols for thetransmission of an ACK/NACK signal. It is assumed that CS indicescorresponding to the respective data OFDM symbols are I_(cs0), I_(cs1),I_(cs2), and I_(cs3).

The modulation symbol d(0) is spread in a cyclic-shifted sequencer(n,I_(cs)). In a slot, assuming that a one-dimensional spread sequencecorresponding to an (i+1)^(th) OFDM symbol is m(i),

it may be represented by {m(0, m(1, m(2, m(3)}={d(0)r(n,I_(cs0),d(0)r(n,I_(cs1), d(0)r(n,I_(cs2), d(0)r(n,I_(cs3))}.

In order to increase a UE capacity, the one-dimensional spread sequencecan be spread using an orthogonal sequence. The following sequence isused as an orthogonal sequence w_(i)(k) (i is a sequence index,0≦k≦K−1), that is, a spreading factor K=4.

TABLE 4 Index (i) [ w_(i)(0), w_(i)(1), w_(i)(2), w_(i)(3) ] 0 [ +1, +1,+1, +1 ] 1 [ +1, −1, +1, −1 ] 2 [ +1, −1, −1, +1 ]

The following sequence is used as the orthogonal sequence w_(i)(k) (i isa sequence index, 0≦k≦K−1), that is, a spreading factor K=3.

TABLE 5 Index (i) [ w_(i)(0), w_(i)(1), w_(i)(2) ] 0 [ +1, +1, +1 ] 1 [+1, e^(j2 π/3), e^(j4 π/3) ] 2 [ +1, e^(j4 π/3), e^(j2 π/3) ]

A different spreading factor can be used for each slot.

Accordingly, when a specific orthogonal sequence index i is given, atwo-dimensional spread sequence {s(0), s(1), s(2), s(3)} can berepresented as follows.

{s(0), s(1), s(2), s(3)}={w_(i)(0)m(0), w_(i)(1)m(1), w_(i)(2)m(2),w_(i)(3)m(3)}

The two-dimensional spread sequences {s(0), s(1), s(2), s(3)} aresubject to an Inverse Fast Fourier Transform (IFFT) and then transmittedin corresponding OFDM symbols. Likewise, an ACK/NACK signal istransmitted on a PUCCH.

The reference signal of the PUCCH format 1b is also spread in anorthogonal sequence by cyclic-shifting a base sequence r(n) and thentransmitted. Assuming that CS indices corresponding to three RS OFDMsymbols are I_(cs4), I_(cs5), and I_(cs6), three cyclic-shiftedsequences r(n,I_(cs4)), r(n,I_(cs6)), and r(n,I_(cs6)) can be obtained.The 3 cyclic-shifted sequences are spread in an orthogonal sequencew^(RS) _(i)(k), that is, K=3.

The orthogonal sequence index i, the CS index I_(cs), and the resourceblock index m are parameters necessary to configure a PUCCH and are alsoresources used to distinguish PUCCHs (or MSs) from one another. If thenumber of available cyclic shifts is 12 and the number of availableorthogonal sequence indices is 3, PUCCHs for a total of 36 MSs can bemultiplexed into one resource block.

In 3GPP LTE, in order for UE to obtain the three parameters forconfiguring a PUCCH, a resource index n⁽¹⁾ _(PUCCH) is defined. Theresource index n⁽¹⁾ _(PUCCH) is defined as n_(CCE)+N⁽¹⁾ _(PUCCI).n_(CCE) is the number of the first CCE used to send corresponding DCI(i.e., downlink resource allocation used to receive downlink datacorresponding to an ACK/NACK signal), and N⁽¹⁾ _(PUCCH) is a parameterthat a BS informs UE through a higher layer message.

Time, frequency, and code resources used to send the ACK/NACK signal arecalled ACK/NACK resources or PUCCH resources. As described above, theindex of ACK/NACK resources (called an ACK/NACK resource index or aPUCCH index) necessary to send the ACK/NACK signal on the PUCCH can berepresented by at least one of the orthogonal sequence index i, the CSindex I_(cs), the resource block index m, and a resources index forcalculating the 3 indices. ACK/NACK resources may include at least oneof an orthogonal sequence, a cyclic shift, a resource block, and acombination of them.

FIG. 8 shows an example of the execution of an HARQ.

UE receives DL resource allocation (or called a DL grant) on a PDCCH 501in an n^(th) DL subframe by monitoring the PDCCH. The UE receives a DLTransport Block (TB) through a PDSCH 502 indicated by the DL resourceallocation.

The UE sends an ACK/NACK signal for the DL transport block on a PUCCH511 in an (n+4)^(th) UL subframe. The ACK/NACK signal may be called anACK/NACK response to the DL transport block.

If the DL transport block is successfully decoded, the ACK/NACK signalbecomes an ACK signal. If the decoding of the DL transport block fails,the ACK/NACK signal becomes a NACK signal. When the NACK signal isreceived, a BS can perform the retransmission of the DL transport blockuntil the ACK signal is received or up to a maximum retransmissionnumber.

In 3GPP LTE, in order to set a resource index for the PUCCH 511, the UEuses the resource allocation of the PDCCH 501. That is, the lowest CCEindex (or the index of the first CCE) used to send the PDCCH 501 becomesn_(CCE), and a resource index is determined like n⁽¹⁾_(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH).

FIG. 9 shows an example of the constellation mapping of an ACK/NACKsignal in the PUCCH formats 1a/1b.

In the PUCCH format 1a, an ACK/NACK signal of 1 bit is transmitted usingBinary Phase Shift Keying (BPSK) as a modulation scheme. In BPSK, NACKis mapped to +1, and ACK is mapped to −1. In the PUCCH format 1b, anACK/NACK signal of 2 bits is transmitted using Quadrature Phase ShiftKeying (QPSK) as a modulation scheme. In QPSK, (ACK, ACK) is mapped to−1, (NACK, NACK) is mapped to +1, (ACK, NACK) is mapped to +j, and(NACK, ACK) is mapped to −j.

In discontinuous transmission (DTX) meaning that UE has failed indetecting a DL grant indicative of resource allocation in a PDCCH, bothACK and NACK are not transmitted. In this case, default NACK results in.DTX is interpreted as NACK by a BS, and DTX generates downlinkretransmission.

Meanwhile, a wireless communication system may be a multi-carriersystem. Here, the multi-carrier system means a system which configures abroadband by aggregating a plurality of carriers each having a smallbandwidth. A 3GPP LTE system supports a case where a downlink bandwidthand an uplink bandwidth are differently set, but one carrier is aprecondition in this case. In contrast, an LTE-A system may be amulti-carrier system using a plurality of Component Carriers (CCs).

A Carrier Aggregation (CA) is used in a multi-carrier system. A CA is tosupport a broadband by aggregating CCs having narrow bands. For example,if five CCs each having a 20 MHz bandwidth are allocated to UE, amaximum of 100 MHz bandwidth can be supported.

A CC or a CC pair can correspond to one cell. Assuming that asynchronization signal and a physical broadcast channel (PBCH) aretransmitted in each CC, one downlink CC (DL CC) may be said tocorrespond to one cell. It may be said that UE communicating with a BSthrough a plurality of CCs is serviced from a plurality of servingcells.

FIG. 10 shows an example of a comparison between the existing singlecarrier system and a multi-carrier system.

Referring to FIG. 10, in a single carrier system, only one carrier issupported for UE in uplink and downlink. A carrier may have a variety ofbandwidths, but the carrier allocated to the UE has one bandwidth. Incontrast, in a multi-carrier system, a plurality of CCs (DL CCs A to Cand UL CCs A to C) can be allocated to UE. For example, in order toallocate a bandwidth of 60 MHz to UE, three CCs each having 20 MHz canbe allocated to the UE.

The number of DL CCs and the number of UL CCs are not limited. A PDCCHand a PDSCH may be independently transmitted in respective DL CCs, and aPUCCH and a PUSCH may be independently transmitted in respective UL CCs.If the number of DL CC-UL CC pairs is defined as 3, it may be said thatUE is serviced from 3 serving cells.

UE can monitor a PDCCH in a plurality of DL CCs and receive downlinktransmission blocks through the plurality of DL CCs at the same time. UEcan send a plurality of uplink transport blocks through a plurality ofUL CCs at the same time, but may have to send HARQ ACK/NACK through onlyone UL CC for a downlink transmission block.

In a multi-carrier system, CC scheduling can include two methods.

In the first method, a PDCCH-PDSCH pair is transmitted in one CC. Thisis called self-scheduling. Furthermore, the self-scheduling means that aPUSCH is transmitted through an UL CC linked to a DL CC in which acorresponding PDCCH is transmitted. That is, the PDCCH allocates thePDSCH resources on the same CC or allocates the PUSCH resources on thelinked UL CC.

In the second method, a DL CC in which a PDSCH is transmitted or an ULCC in which a PUSCH is transmitted are determined irrespective of a DLCC in which a PDCCH is transmitted. That is, the PDCCH and the PDSCH aretransmitted in different DL CCs, or the PUSCH is transmitted through anUL CC not linked to the DL CC in which the PDCCH has been transmitted.This is called cross-carrier scheduling.

A CC in which the PDCCH is transmitted is called a PDCCH carrier, amonitoring carrier, or a scheduling carrier. A CC in which the PDSCH orPUSCH is transmitted is called a PDSCH or PUSCH carrier or a scheduledcarrier.

In order for data to be transmitted and received through a specificcell, UE has to first complete a configuration for the specific cell.Here, the configuration means a state in which the reception of systeminformation necessary to transmit and receive the data for the specificcell has been completed. For example, the configuration may include anoverall process of receiving common physical layer parameters necessaryto transmit and receive data, MAC layer parameters, or parametersnecessary for a specific operation in an RRC layer. Aconfiguration-complete cell becomes a state in which the cell cantransmit and receive data immediately when the cell receives onlyinformation on which the data can be transmitted.

A cell of a configuration-complete state may be present in an activationor deactivation state. Here, activation refers to a state in whichtransmission or reception is being performed or a state in whichtransmission or reception is ready. UE can monitor or receive thecontrol channel (PDCCH) and the data channel (PDSCH) of an activatedcell in order to check resources allocated thereto (e.g., a frequencyand time).

Deactivation means that the transmission or reception of traffic data isimpossible and that measurement or the transmission/reception of minimuminformation is possible. UE can receive necessary System Information(SI) in order to receive a packet from a deactivated cell. In contrast,UE does not monitor or receive the control channel (PDCCH) and the datachannel (PDSCH) of a deactivated cell in order to check resourcesallocated thereto (e.g., a frequency and time).

A cell may be divided into a primary cell and a secondary cell (or aserving cell).

The primary cell means a cell that operates in a primary frequency, acell through which UE performs an initial connection establishmentprocedure or a connection re-establishment process with a BS, or a cellindicated as a primary cell in a handover process.

The secondary cell means a cell that operates in a secondary frequency.Once RRC connection is set up, the secondary cell is used to provideadditional radio resources.

A serving cell is configured as a primary cell in the case of UE inwhich a CA has not been configured or UE to which a CA cannot beprovided. If a CA is configured, the term ‘serving cell’ is used toindicate a primary cell, one of all secondary cells, or a set of aplurality of cells. A downlink CC may configure one serving cell, or adownlink CC and an uplink CC may form one serving cell throughconnection establishment. However, a serving cell does not include onlyone uplink CC.

That is, a primary cell means one serving cell that provides a securityinput and NAS mobility information in an RRC establishment orre-establishment state. At least one cell, together with a primary cell,may form a set of serving cells depending on the capabilities of UE.Here, at least one cell is called a secondary cell. Accordingly, a setof serving cells configured for one MS may include only one primary cellor may include one primary cell and at least one secondary cell.

A Primary Component Carrier (PCC) means a CC corresponding to a primarycell. The PCC is a CC through which UE sets up connection or RRCconnection with a BS at the early stage, from among some CCs. The PCC isa CC that is responsible for connection or RRC connection for signalingregarding a plurality of CCs and that manages UE context, that is,connection information related to UE. Furthermore, the PCC is alwayspresent in an activation state when it is connected with UE and thus inRRC connected mode.

A Secondary Component Carrier (SCC) means a CC corresponding to asecondary cell. That is, the SCC is a CC allocated to UE in addition toa PCC. The SCC is a carrier that has been extended for additionalresource allocation by UE in addition to a PCC and may be divided intoactivation and deactivation states.

A downlink CC corresponding to a primary cell is called a downlinkPrimary Component Carrier (DL PCC), and an uplink CC corresponding to aprimary cell is called an UL PCC. Furthermore, in downlink, a CCcorresponding to a secondary cell is called a DL Secondary CC (DL SCC).In uplink, a CC corresponding to a secondary cell is called an UL SCC.

A primary cell and a secondary cell have the following characteristics.

First, the primary cell is used to send a PUCCH.

Second, the primary cell is always activated, whereas the secondary cellis a carrier that is activated or deactivated depending on a specificcondition.

Third, when the primary cell experiences a Radio Link Failure(hereinafter referred to as an RLF), RRC re-establishment is triggered.When the secondary cell experiences an RLF, RRC re-establishment is nottriggered.

Fourth, the primary cell can be changed by a change of a security key ora handover procedure that is accompanied by a Random Access Channel(RACH) procedure.

Fifth, Non-Access Stratum (NAS) information is received through theprimary cell.

Sixth, in the primary cell, a DL PCC and an UL PCC are always configuredin pair.

Seventh, a different Component Carrier (CC) can be configured as aprimary cell for each UE.

Eighth, procedures, such as the reconfiguration, addition, and removalof a primary cell, can be performed by an RRC layer. In adding a newsecondary cell, RRC signaling may be used to send system information ona dedicated secondary cell.

The activation/deactivation of a component carrier is equal to theactivation/deactivation of a serving cell. For example, assuming that aserving cell1 is composed of a DL CC1, the activation of the servingcell1 means the activation of the DL CC1. Assuming that a DL CC2 and anUL CC2 have been subject to connection established in a serving cell2,the activation of the serving cell2 means the activation of the DL CC2and the UL CC2. In this sense each component carrier can correspond to acell.

The number of aggregated component carriers may be differently set indownlink and uplink. A case where the number of downlink CCs is equal tothe number of uplink CCs is called a symmetric aggregation, and a casewhere the number of downlink CCs is different from the number of uplinkCCs is called an asymmetric aggregation. Furthermore, CCs may havedifferent sizes (i.e., bandwidths). For example, assuming that 5 CCs areused to configure a 70 MHz band, the 5 CCs may be configured like a 5MHz CC (a carrier #0)+a 20 MHz CC (a carrier #1)+a 20 MHz CC (a carrier#2)+a 20 MHz CC (a carrier #3)+a 5 MHz CC (a carrier #4).

As described above, in a multi-carrier system, unlike in a singlecarrier system, a plurality of Component Carriers (CCs), that is, aplurality of serving cells, can be supported. Accordingly, one MS canreceive a plurality of PDSCHs through a plurality of DL CCs.Furthermore, UE can send ACK/NACK for a plurality of PDSCHs through oneUL CC, for example, an UL PCC. That is, in a conventional single carriersystem, a maximum of two pieces of HARQ ACK/NACK (hereinafterabbreviated as ACK/NACK, for the sake of convenience) information hasonly to be transmitted because only one PDSCH is received in onesubframe. In a multi-carrier system, however, there is a need for anACK/NACK transmission method because ACK/NACK for a plurality of PDSCHscan be transmitted through one UL CC.

One of methods for sending a plurality of ACK/NACKs includes channelselection. The channel selection method is a method of transmittingACK/NACK information using radio resources used to send a signal and aconstellation point according to a bit value that is transmitted in theradio resources.

FIG. 11 shows an example of channel selection for ACK/NACK informationof 2 bits.

Referring to FIG. 11( a), R1 and R2 mean respective PUCCH resources.2-bit ACK/NACK information is mapped to a point on the signalconstellation of a modulation symbol that has been BPSK-modulated ineach PUCCH resource. For example, if a point on the signal constellationof a modulation symbol corresponds to +1 in the R1 resource, it may mean(NACK, NACK). If a point on the signal constellation of a modulationsymbol corresponds to −1 in the R1 resource, it may mean (ACK, NACK). Ifa point on the signal constellation of a modulation symbol correspondsto +1 in the R2 resource, it may mean (NACK, ACK). If a point on thesignal constellation of a modulation symbol corresponds to −1 in the R2resource, it may mean (ACK, ACK). As described above, the four states ofACK/NACK can be represented using two PUCCH resources and BPSK symbols.

Referring to FIG. 11( b), R1 means a PUCCH resource, and 2-bit ACK/NACKinformation may be determined depending on a point on the signalconstellation of a QPSK-modulated symbol. That is, if the position ofthe QPSK-modulated symbol is +1, it may mean (NACK, NACK). If theposition of the QPSK-modulated symbol is −1, it may mean (ACK, ACK). Ifthe position of the QPSK-modulated symbol is +j, it may mean (ACK,NACK). If the position of the QPSK-modulated symbol is −j, it may mean(NACK, ACK).

In FIG. 11, the above-described 2-bit ACK/NACK information may beACK/NACK for two DL CCs in which MIMO transmission is not performed in amulti-carrier system.

Channel selection for 3-bit ACK/NACK information and 4-bit ACK/NACKinformation is described below. The 3-bit ACK/NACK information may beACK/NACK for one DL CC in which MIMO transmission is not performed(hereinafter referred to as a NON-MIMO DL CC) and one DL CC in whichMIMO transmission is performed (hereinafter referred to as a MIMO DLCC). Or, the 3-bit ACK/NACK information may be ACK/NACK for three DL CCsin which MIMO transmission is not performed. The 4-bit ACK/NACKinformation may be ACK/NACK for two MIMO DL CCs, ACK/NACK for twoNON-MIMO DL CCs and one MIMO DL CC, or ACK/NACK for four NON-MIMO DLCCs.

FIG. 12 illustrates channel selection for 3-bit ACK/NACK information.

Referring to FIG. 12, eight ACK/NACK information states can berepresented using two PUCCH resources, such as R1 and R2, and the pointsof four signal constellations in the respective PUCCH resources. Forexample, if a point on the signal constellation of a modulation symbolcorresponds to +1 in the R1 resource, it may mean (NACK, NACK, ACK). Ifa point on the signal constellation of a modulation symbol correspondsto −1 in the R1 resource, it may mean (NACK, ACK, ACK). If a point onthe signal constellation of a modulation symbol corresponds to +j in theR1 resource, it may mean (NACK, ACK, NACK). If a point on the signalconstellation of a modulation symbol corresponds to −j in the R1resource, it may mean (NACK, NACK, ACK).

FIG. 13 is an example illustrating objects indicated by the respectivebits of 3-bit ACK/NACK information and channel selection for the 3-bitACK/NACK information.

For example, a case where ACK/NACK for one MIMO DL CC in which UE cansend one NON-MIMO DL CC and two codewords is assumed below. Here, the UEmay classify the ACK/NACK for the MIMO DL CC into a point on the signalconstellation of a QPSK modulation symbol and ACK/NACK for a NON-MIMO DLCC into what PUCCH resources. That is, if transmission is performed inan R1 resource, it may be classified as NACK. If transmission isperformed in an R2 resource, it may be classified as ACK.

In order to use this method, the 3-bit ACK/NACK information may bemapped so that a Most Significant Bit (MSB) indicates 1-bit ACK/NACK fora NON-MIMO DL CC and 2 bits including a Least Significant Bit (LSB)indicate 2-bit ACK/NACK for an MIMO DL CC, as shown in FIG. 13.

FIG. 14 is another example illustrating a mapping relationship withobjects indicated by the respective bits of 3-bit ACK/NACK information.A case where ACK/NACK for one MIMO DL CC in which UE can send oneNON-MIMO DL CC and two codeword is assumed below.

Referring to FIG. 14, in the 3-bit ACK/NACK information, an MSBindicates ACK/NACK for a codeword (CW) #2 for the MIMO DL CC, a next bitindicates ACK/NACK for a codeword #1 for the MIMO DL CC, and an LSBindicates ACK/NACK for the NON-MIMO DL CC. That is, if two DL CCs havebeen configured in UE, ACK/NACKs for one codeword (i.e., the codeword #1of the MIMO DL CC and the codeword of the NON-MIMO DL CC) are classifiedinto points on the signal constellation of a QPSK modulation symbol andACK/NACK for the remaining codeword (i.e., the codeword #2 of the MIMODL CC) is classified through a PUCCH resource, in the respective DL CCs.

FIG. 15 illustrates channel selection for ACK/NACK information of 4bits.

Referring to FIG. 15, R1, R2, R3, and R4 indicate four PUCCH resources.In each of the PUCCH resources, the states of 4-bit ACK/NACK informationare indicated depending on four constellation points. Accordingly, atotal of 16 states of ACK/NACK information can be represented.

FIG. 16 shows examples illustrating a mapping relationship with objectsindicated by the respective bits of 4-bit ACK/NACK information.

In FIG. 16( a), a case where two NON-MIMO DL CCs and one MIMO DL CC thatsupports up to codewords are configured in UE is assumed below. Here, inthe 4-bit ACK/NACK information, an MSB to 2 bits may indicate ACK/NACKfor the two NON-MIMO DL CCs, and an LSB to 2 bits may indicate ACK/NACKfor the two codewords transmitted in the one MIMO DL CC.

In FIG. 16( b), a case where two MIMO DL CCs supporting up to twocodewords have been configured in UE is assumed below. Here, in the4-bit ACK/NACK information, an MSB to 2 bits may indicate ACK/NACK forthe two codewords transmitted in any one MIMO DL CC, and an LSB to 2bits may indicate ACK/NACK for the two codewords transmitted in theremaining MIMO DL CC.

FIG. 17 shows mapping to radio resources and constellation points when4-bit ACK/NACK information is information, such as that shown in FIG.16.

Referring to FIG. 17, pieces of information classified as fourconstellation points in PUCCH resources R1, R2, R3, and R4 are ACK/NACKsfor two codewords transmitted in a MIMO DL CC. In a mappingrelationship, such as that shown in FIG. 16( a), ACK/NACK for twoNON-MIMO DL CCs can be known depending on whether the ACK/NACK istransmitted in what PUCCH resource. In a mapping relationship, such asthat shown in FIG. 16( b), ACK/NACK for two codewords transmitted in oneMIMO DL CC can be known depending on whether the ACK/NACK is transmittedin what PUCCH resource.

FIG. 18 is another example illustrating a mapping relationship withobjects indicated by respective bits in 4-bit ACK/NACK information andmapping to radio resources and constellation points. A case where twoMIMO DL CCs supporting up to two codewords, that is, a MIMO DL CC1 and aMIMO DL CC2, have been configured in UE is assumed below.

Referring to FIG. 18, in the 4-bit ACK/NACK information, an MSB to thecodeword #2 of the MIMO DL CC 1, the codeword #2 of the MIMO DL CC 2,the codeword #1 of the MIMO DL CC 1, and the codeword #1 of the MIMO DLCC 2 can be sequentially represented.

As described above, channel selection for sending a plurality ofACK/NACKs can be implemented using a variety of methods. In amulti-carrier system, however, although a specific DL CC is set in MIMOmode, a BS can send only one codeword dynamically depending on itsselection. In this case, how UE will send ACK/NACK for one codeword maybe problematic.

Channel selection can be determined by the number of configured DL CCsand mode set in each DL CC (i.e., it is MIMO mode or NON-MIMO mode). Ifa BS changes the configuration of DL CCs, that is, the number of DL CCsor the transmission mode of the DL CCs of UE, however, a reconfigurationperiod for changing the configuration may be present. In thereconfiguration period, pieces of configuration information areexchanged between the BS and the UE. The BS can transfer configurationinformation through only a DL PCC in the reconfiguration period. In thiscase, if there is a difference between ACK/NACK channel selection for aDL PCC used by the UE and ACK/NACK channel selection for a DL PCCexpected by the BS, a severe error may occur. Accordingly, it ispreferred that a mismatch do not occur in the ACK/NACK channel selectionin a process of changing or reconfiguring the configuration of the DLCCs between the BS and the UE. To this end, in ACK/NACK channelselection transmitted when UE receives a PDSCH through only a DL PCC,points on the same signal constellation as those of the PUCCH format 1aor the PUCCH format 1b are preferably used.

A method in which UE in which two DL CCs (i.e., two serving cells) havebeen configured sends HARQ ACK/NACK is described below. This methodrelates to a method of transmitting ACK/NACK when UE receives only onetransport block through a DL CC in a situation that the DL CC isconfigured in transmission mode supporting up to two transport blocks.

FIG. 19 is the ACK/NACK transmission method of UE in accordance with anembodiment of the present invention.

Referring to FIG. 19, the UE receives a first transport block from a BSthrough a first serving cell (S100) and receives a second transportblock through a second serving cell (S200). Here, it is assumed that thefirst serving cell is set in a first transmission mode which supports upto two transport blocks.

The UE determines a first response to the first transport block and asecond response to the second transport block (S300) and sends an HARQACK/NACK response according to the first response and the secondresponse to the BS at step S400.

Here, the first response is the same as a response in the case where thefirst serving cell has received all the two transport blocks and hassuccessfully decoded the two transport blocks if the first transportblock has been successfully decoded. Or, the first response is the sameas a response in the case where the first serving cell has notsuccessfully decoded all the two transport blocks if the first transportblock has not been successfully decoded.

FIGS. 20 to 22 show examples in which UE uses channel selection when onetransport block is received in a serving cell which supports up to twotransport blocks.

FIG. 20 shows an example of channel selection when only one transportblock (codeword) is received in a MIMO DL CC if one NON-MEMO DL CC andone MIMO DL CC supporting up to two codewords (transport blocks) havebeen configured in UE. FIG. 21 shows an example of channel selectionwhen only one codeword (transport block) is received in a MIMO DL CC iftwo NON-MIMO DL CCs and one MIMO DL CC supporting up to two codewordshave been configured in UE.

In FIGS. 20 and 21, when the UE receives the two transport blocks in theMIMO DL CC, ACK/NACKs for the two transport blocks are distinguishedbased on a point on a signal constellation in each PUCCH resource. Whenthe UE receives only one transport block in the MIMO DL CC, if the onetransport block is successfully decoded, it is mapped to a point on thesame signal constellation as that of a case where both the two transportblocks have been received in the MIMO DL CC and successfully decoded.Furthermore, if the one transport block has not been successfullydecoded, it is mapped to a point on the same signal constellation asthat of a case where the two transport blocks have been received in theMIMO DL CC and both have not been successfully decoded. That is, the UEinterprets ACK for one transport block received in the MIMO DL CC as(ACK, ACK), performs mapping, interprets NACK as (NACK, NACK), andperforms mapping. Here, ACK/NACK for the codeword of a NON-MIMO DL CC isdistinguished depending on the ACK/NACK is transmitted through whatPUCCH resources. According to this method, the reception performance ofACK/NACK of a BS can be improved because points on the signalconstellation of an ACK/NACK response are spaced apart from each otherto a maximum extend, as shown in FIGS. 20 and 21.

FIG. 22 shows yet another example of channel selection when only onetransport block (codeword) is received in a MIMO DL CC. A case where twoMIMO DL CCs supporting up to two codewords have been configured in UE isassumed below.

If only one transport block has been received in a MIMO DL CC1 and hasbeen successfully decoded, the UE sends an HARQ ACK/NACK response likein a case where all the two transport blocks have been received in theMIMO DL CC1 and have been successfully decoded. If only one transportblock has been received in the MIMO DL CC1 and has not been successfullydecoded, the UE sends an HARQ ACK/NACK response like in a case where allthe two transport blocks have been received in the MIMO DL CC1 and havenot been successfully decoded. Here, ACK/NACK for the two transportblocks that have been received in a MIMO DL CC2 can be distinguisheddepending on a point on the signal constellation in each PUCCH resource.According to this method, as shown in FIG. 22, only PUCCH resources R1and R4 can be used. That is, ACK/NACK for the MIMO DL CC1 can betransmitted using two PUCCH resources that have been spaced from eachother to a maximum extent (i.e., PUCCH resources in which a differencebetween their resource indices is a maximum or a difference betweencyclic shifts and/or orthogonal spreading codes used in resources is amaximum).

Detailed embodiments to which the above-described channel selectionmethods are applied are described below.

For example, in a multi-carrier system using FDD, UE can feed backACK/NACK for two configured serving cells using the PUCCH format 1b thatuses channel selection.

The UE can feed ACK/NACK for a maximum of up to two transport blocks,received in one serving cell, back to a BS by sending 2-bits (b(0)b(1)information in one PUCCH resource selected from a plurality of PUCCHresources. One codeword can be transmitted in one transport block. Signsare described in order to clarify a description. A PUCCH resource can berepresented by a resource index n⁽¹⁾ _(PUCCH,i). Here, A is any one of{2, 3, 4}, and i is 0≦i≦(A−1). 2-bit information is represented byb(0)b(1).

HARQ-ACK(j) indicates an HARQ ACK/NACK response related to a transportblock or an SPS release PDCCH that is transmitted by a serving cell. TheHARQ-ACK(j), the serving cell, and the transport block may have thefollowing mapping relationship.

TABLE 6 HARQ-ACK(J) A HARQ-ACK(0) HARQ-ACK(1) HARQ-ACK(2) HARQ-ACK(3) 2TRANSPORT TRANSPORT NA NA BLOCK 1 OF BLOCK 2 OF PRIMARY SECONDARY CELLCELL 3 TRANSPORT TRANSPORT TRANSPORT NA BLOCK 1 OF BLOCK 2 OF BLOCK 3 OFSERVING SERVING SERVING CELL 1 CELL 1 CELL 2 4 TRANSPORT TRANSPORTTRANSPORT TRANSPORT BLOCK 1 OF BLOCK 2 OF BLOCK 3 OF BLOCK 4 OF PRIMARYPRIMARY SECONDARY SECONDARY CELL CELL CELL CELL

In Table 6, for example, in the case of A=4, HARQ-ACK(0) and HARQ-ACK(1)indicate ACK/NACKs for two transport blocks transmitted by a primarycell, and HARQ-ACK(2) and HARQ-ACK(3) indicate ACK/NACKs for twotransport blocks transmitted by a secondary cell.

When UE receive a PDSCH by detecting a PDCCH in the subframe (n−4) ofthe primary cell or detects an SPS release PDCCH, the UE sends ACK/NACKusing a PUCCH resource n⁽¹⁾ _(PUCCH,i). Here, n⁽¹⁾ _(PUCCH,i) isdetermined as n_(CCE,i)+N⁽²⁾ _(PUCCH). Here, n_(CCE,i) means the indexof the first CCE that is used for a BS to send the PDCCH, and N⁽¹⁾_(PUCCH) is a value set through a higher layer signal. If thetransmission mode of the primary cell supports up to two transportblocks, a PUCCH resources n⁽¹⁾ _(PUCCH,i+1) is given. n⁽¹⁾ _(PUCCH,i+1)can be determined as n_(CCE,i)+1+N⁽¹⁾ _(PUCCH). That is, if the primarycell is set in transmission mode in which a maximum of up to twotransport blocks can be transmitted, two PUCCH resources can bedetermined.

If there is no PDCCH detected in the subframe (n−4) of the primary cell,the PUCCH resource n⁽¹⁾ _(PUCCH,i) for sending ACK/NACK to the PDSCH isdetermined by a higher layer configuration. If up to two transportblocks are supported, the PUCCH resource n⁽¹⁾ _(PUCCH,i+1) can be givenas n⁽¹⁾ _(PUCCH,i+1)=n⁽¹⁾ _(PUCHH,i)+1.

If the PDCCH is detected in the subframe (n−4) and the PDSCH is receivedfrom the secondary cell, the PUCCH resources n⁽¹⁾ _(PUCCH,i) and n⁽¹⁾_(PUCCH,i+1) for the transmission mode that supports up to two transportblocks can be determined by a higher layer configuration.

The following table shows a relationship between ACK/NACK, PUCCHresources, and 2-bit information of b(0)b(1) in the PUCCH format 1b inwhich channel selection is used for two PUCCH resources (when A=2).

TABLE 7 HARQ-ACK(0) HARQ-ACK(1) n_(PUCCH,i) ⁽¹⁾ b(0)b(1) ACK ACKn_(PUCCH,1) ⁽¹⁾ 1,1 ACK NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,1 NACK/DTX ACKn_(PUCCH,1) ⁽¹⁾ 0,0 NACK NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0,0 DTX NACK/DTX NoTransmission

The following table shows a relationship between ACK/NACK, PUCCHresources, and 2-bit information in the PUCCH format 1b in which channelselection is used for three PUCCH resources (when A=3).

TABLE 8 HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2) n_(PUCCH,i) ⁽¹⁾ b(0)b(1)ACK ACK ACK n_(PUCCH,1) ⁽¹⁾ 1,1 ACK NACK/DTX ACK n_(PUCCH,1) ⁽¹⁾ 1,0NACK/DTX ACK ACK n_(PUCCH,1) ⁽¹⁾ 0,1 NACK/DTX NACK/DTX ACK n_(PUCCH,2)⁽¹⁾ 1,1 ACK ACK NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,1 ACK NACK/DTX NACK/DTXn_(PUCCH,0) ⁽¹⁾ 1,0 NACK/DTX ACK NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0,1 NACK/DTXNACK/DTX NACK n_(PUCCH,2) ⁽¹⁾ 0,0 NACK NACK/DTX DTX n_(PUCCH,0) ⁽¹⁾ 0,0NACK/DTX NACK DTX n_(PUCCH,0) ⁽¹⁾ 0,0 DTX DTX DTX No Transmission

If a DL PCC has been set in MIMO mode in the state in which two DL CCsDL PCC and DL SCC have been configured in UE and two codeword PDSCHs arereceived in the DL PCC, HARQ-ACK(0) and HARQ-ACK(1) may have to be fedback. Furthermore, if one codeword PDSCH is received in the DL PCC, theUE can determine (HARQ-ACK(0), HARQ-ACK(1)) as (ACK, ACK) or (NACK,NACK) and send them as in the following table.

TABLE 9 HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2) n_(PUCCH,i) ⁽¹⁾ b(0)b(1)ACK ACK NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,1 NACK NACK/DTX DTX n_(PUCCH,0) ⁽¹⁾0,0 NACK/DTX NACK/DTX ACK n_(PUCCH,2) ⁽¹⁾ 1,1 NACK/DTX NACK/DTX NACKn_(PUCCH,2) ⁽¹⁾ 0,0

The following table shows a relationship between ACK/NACK, PUCCHresources, and 2-bit information in the PUCCH format 1b in which channelselection is used for four PUCCH resources (when A=4).

TABLE 10 HARQ- HARQ- HARQ- HARQ- b(0) ACK(0) ACK(1) ACK(2) ACK(3)n_(PUCCH,i) ⁽¹⁾ b(1) ACK ACK ACK ACK n_(PUCCH,1) ⁽¹⁾ 1,1 ACK NACK/DTXACK ACK n_(PUCCH,2) ⁽¹⁾ 0,1 NACK/DTX ACK ACK ACK n_(PUCCH,1) ⁽¹⁾ 0,1NACK/DTX NACK/DTX ACK ACK n_(PUCCH,3) ⁽¹⁾ 1,1 ACK ACK ACK NACK/DTXn_(PUCCH,1) ⁽¹⁾ 1,0 ACK NACK/DTX ACK NACK/DTX n_(PUCCH,2) ⁽¹⁾ 0,0NACK/DTX ACK ACK NACK/DTX n_(PUCCH,1) ⁽¹⁾ 0,0 NACK/DTX NACK/DTX ACKNACK/DTX n_(PUCCH,3) ⁽¹⁾ 1,0 ACK ACK NACK/DTX ACK n_(PUCCH,2) ⁽¹⁾ 1,1ACK NACK/DTX NACK/DTX ACK n_(PUCCH,2) ⁽¹⁾ 1,0 NACK/DTX ACK NACK/DTX ACKn_(PUCCH,3) ⁽¹⁾ 0,1 NACK/DTX NACK/DTX NACK/DTX ACK n_(PUCCH,3) ⁽¹⁾ 0,0ACK ACK NACK/DTX NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,1 ACK NACK/DTX NACK/DTXNACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,0 NACK/DTX ACK NACK/DTX NACK/DTX n_(PUCCH,0)⁽¹⁾ 0,1 NACK/DTX NACK NACK/DTX NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0,0 NACKNACK/DTX NACK/DTX NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0,0 DTX DTX NACK/DTX NACK/DTXNo Transmission

If a DL PCC and a DL SCC have been configured in MIMO mode in the statein which two DL CCs DL PCC and DL SCC have been configured in UE and onecodeword PDSCH is received in the DL PCC or the DL SCC, the UE may send(HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), HARQ-ACK(3)) as in the followingtable.

TABLE 11 HARQ- HARQ- HARQ- HARQ- b(0) ACK(0) ACK(1) ACK(2) ACK(3)n_(PUCCH,i) ⁽¹⁾ b(1) ACK ACK NACK/DTX NACK/DTX n_(PUCCH,0) ⁽¹⁾ 1,1NACK/DTX NACK NACK/DTX NACK/DTX n_(PUCCH,0) ⁽¹⁾ 0,0 ACK ACK ACK ACKn_(PUCCH,1) ⁽¹⁾ 1,1 NACK/DTX NACK/DTX ACK ACK n_(PUCCH,3) ⁽¹⁾ 1,1 ACKACK ACK NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1,0 NACK/DTX NACK/DTX ACK NACK/DTXn_(PUCCH,3) ⁽¹⁾ 1,0 ACK ACK NACK/DTX ACK n_(PUCCH,2) ⁽¹⁾ 1,1 NACK/DTXNACK/DTX NACK/DTX ACK n_(PUCCH,3) ⁽¹⁾ 0,0

That is, if UE receives only one transport block from a serving cellthat has been set in transmission mode supporting up to two transportblocks, the UE uses 4-bit ACK/NACK (HARQ-ACK(0), HARQ-ACK(1),HARQ-ACK(2), HARQ-ACK(3)) channel selection irrespective of the numberof transport blocks actually received and uses the same HARQ ACK/NACKresponses as that of a case where the two transport blocks have beenreceived from the serving cell for the received one transport block.Here, if the decoding of the one transport block is successful, (ACK,ACK) is used. If the decoding of the one transport block fails, (NACK,NACK) is used.

In other words, if only a single codeword has been dynamically receivedin a MIMO DL CC set in MIMO mode, ACK/NACK information for thecorresponding codeword may be represented as copying the ACK/NACKinformation of the single codeword. That is, repetitive transmission maybe represented like (ACK, ACK) if ACK has to be transmitted for thesingle codeword and (NACK, NACK) if NACK has to be transmitted for thesingle codeword.

This method may be extended and applied to a case where UE receives aPDCCH in which an SPS release command is carried in a MIMO DL CC. Thatis, if the SPS release PDCCH is received in the MIMO DL CC, ACK isinterpreted as (ACK, ACK) and NACK is interpreted as (NACK, NACK) when1-bit ACK/NACK information is sent, and the SPS release PDCCH is carriedon a 2-bit point and transmitted.

If a DL PCC is set in MIMO mode in an environment in which UE hasaggregated and used two DL CCs, when two codeword PDSCHs are received inthe DL PCC in order to support the existing LTE Rel-8/9 fallbackfunction, mapping on a signal constellation of 2-bit ACK/NACK may bemapping, such as that of the PUCCH format 1b of Rel-8. Furthermore, whenone codeword PDSCH is received in the DL PCC set in MIMO mode, mappingon a signal constellation of 1-bit ACK/NACK for the one codeword PDSCHmay have the same mapping as that of the PUCCH format 1a of Rel-8 (ACKfor one codeword PDSCH is mapped to (ACK, ACK) for two codeword PDSCHsand NACK for one codeword PDSCH is mapped to (NACK, NACK) for twocodeword PDSCHs). In this case, Rel-8 fallback can be performedirrespective of whether the PDSCH received in the DL PCC is a singlecodeword or two codewords.

FIG. 23 is a block diagram showing a BS and UE in which an embodiment ofthe present invention is implemented.

A BS 100 includes a processor 110, memory 120, and a Radio Frequency(RF) unit 130. The processor 110 implements the proposed functions,processes and/or methods. For example, the processor 110 configuresserving cells in UE and provides configuration information on thetransmission mode of each serving cell. Furthermore, the processor 110sends a transport block to UE through the serving cell and receives HARQACK/NACK feedback. The layers of a radio interface protocol can beimplemented by the processor 110. The memory 120 is connected to theprocessor 110, and the memory 120 stores a variety of pieces ofinformation for driving the processor 110. The RF unit 130 is connectedto the processor 110, and the RF unit 130 sends and/or receives radiosignals.

The UE 200 includes a processor 210, memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, processes and/ormethods. The layers of a radio interface protocol can be implemented bythe processor 210. The processor 210 receives a first transport blockthrough a first serving cell set in a first transmission mode thatsupports up to two transport blocks and receives at least one secondtransport block through a second serving cell set in a secondtransmission mode. Next, the processor 210 determines an HARQ ACK/NACKresponse, including a first response to the first transport block and asecond response to the at least one second transport block, and sendsthe HARQ ACK/NACK response to a BS. Here, the first response included inthe HARQ ACK/NACK response is identical with a response used when twotransport blocks are received through the first serving cell. Forexample, if the first transport block is successfully decoded, (ACK,ACK) is transmitted like in a case where the two transport blocks havebeen successfully decoded in the first serving cell. If the decoding ofthe first transport block fails, (NACK, NACK) is transmitted like in acase where both the two transport blocks have not been successfullydecoded in the first serving cell. The memory 220 is connected to theprocessor 210, and the memory 220 stores a variety of pieces ofinformation for driving the processor 210. The RF unit 230 is connectedto the processor 210, and the RF unit 230 sends and/or receives radiosignals and sends the spread complex modulation symbols to a BS.

The processor 110, 210 may include Application-Specific IntegratedCircuits (ASICs), other chipsets, logic circuits and/or data processors.The memory 120, 220 may include Read-Only Memory (ROM), Random AccessMemory (RAM), flash memory, memory cards, storage media and/or otherstorage devices. The RF unit 130, 230 may include a baseband circuit forprocessing radio signals. When the embodiment is implemented insoftware, the above-described scheme may be implemented into a module(process or function) that performs the above function. The module maybe stored in the memory 120, 220 and executed by the processor 110, 210.The memory 120, 220 may be placed inside or outside the processor 110,210 and connected to the processor 110, 210 using a variety ofwell-known means. In the above exemplary systems, although the methodshave been described on the basis of the flowcharts using a series of thesteps or blocks, the present invention is not limited to the sequence ofthe steps, and some of the steps may be performed at different sequencesfrom the remaining steps or may be performed simultaneously with theremaining steps. Furthermore, those skilled in the art will understandthat the steps shown in the flowcharts are not exclusive and other stepsmay be included or one or more steps of the flowcharts may be deletedwithout affecting the scope of the present invention.

The above embodiments include various aspects of examples. Although allpossible combinations for describing the various aspects may not bedescribed, those skilled in the art may appreciate that othercombinations are possible. Accordingly, the present invention should beconstrued as including all other replacements, modifications, andchanges which fall within the scope of the claims.

1. A method of transmitting hybrid automatic repeat request (HARQ)acknowledgement/not-acknowledgement (ACK/NACK) response for a userequipment (UE) configured with two serving cells including a firstserving cell and a second serving cell, the method comprising: receivinga first transport block (TB) through the first serving cell configuredwith a first transmission mode that supports up to two transmissionblocks; and transmitting a HARQ ACK/NACK response including a firstresponse for the first transport block, wherein the first response is asame response used in case two transport blocks are received through thefirst serving cell.
 2. The method of claim 1, wherein in case the firsttransport block is decoded successfully, the first response is a sameresponse used in case two transport blocks are received through thefirst serving cell and the two transport blocks are decodedsuccessfully.
 3. The method of claim 1, wherein in case the firsttransport block is not decoded successfully, the first response is asame response used in case two transport blocks are received through thefirst serving cell and the two transport blocks are not decodedsuccessfully.
 4. The method of claim 1, further comprising: receiving atleast one second transport block through the second serving cellconfigured with a second transmission mode, wherein the HARQ ACK/NACKresponse comprises the first response and a second response for the atleast one second transport block.
 5. The method of claim 4, furthercomprising: determining two uplink resources for the first transportblock; determining at least one uplink resource for the at least onesecond transport block; selecting one uplink resource among the twouplink resources and the at least one uplink resource according to thefirst response and the second response; and transmitting information of2 bits through the selected one uplink resource.
 6. The method of claim5, wherein if the first serving cell is a primary cell, the two uplinkresources are determined based on a resource used for a physicaldownlink control channel (PDCCH), transmitted through the first servingcell, carrying a resource allocation information for the first transportblock.
 7. The method of claim 6, wherein if the second serving cell is asecondary cell, the at least one uplink resource is determined based ona resource value determined by a PDCCH transmitted through the secondserving cell among four resource values configured by higher layers. 8.The method of claim 5, wherein the information of 2 bits is modulated byquadrature phase shift keying (QPSK) and transmitted.
 9. The method ofclaim 5, wherein if the second transmission mode is transmission modesupporting up to two transport blocks and a second transport block isreceived through the second serving cell and is successfully decoded,the second response is a same response used in case two transport blocksare received through the second serving cell and the two transportblocks are successfully decoded.
 10. The method of claim 5, wherein ifthe second transmission mode is transmission mode supporting up to twotransport blocks and a second transport block is received through thesecond serving cell and is not successfully decoded, the second responseis a same response used in case two transport blocks are receivedthrough the second serving cell and the two transport blocks are notsuccessfully decoded.
 11. The method of claim 1, wherein the firstserving cell is a primary cell through which the user equipment performsan initial connection establishment process or a connectionre-establishment process with a base station.
 12. The method of claim 1,wherein the two serving cells operate in Frequency Division Duplex(FDD).
 13. User equipment, comprising: a Radio Frequency (RF) unitconfigured to send or receive radio signals; and a processor connectedto the RF unit, and configured to receive a first transport block (TB)through the first serving cell configured with a first transmission modethat supports up to two transmission blocks, and transmit a HARQACK/NACK response including a first response for the first transportblock, wherein the first response is a same response used in case twotransport blocks are received through the first serving cell.
 14. Theuser equipment of claim 13, wherein: the processor is further configuredto receive at least one second transport block through the secondserving cell configured with a second transmission mode, and wherein theHARQ ACK/NACK response comprises the first response and a secondresponse for the at least one second transport block.